Put it on your 5.56 lower and use a .410 mag and you have a semi auto shotty.

obviously a .410 is less effective than a 5.56/.223 BUT the cool factor is there. You have the choice of .410 slugs, PDX or other home defense ammo, buckshot, and birdshot.

A lot of versatility there. the slugs run about 1800fps, the buck shot give great penetration, actually better than a 5.56 as it does not tend to fragment as many 5.56 rounds do. PDX is a beast at close range. The slugs deliver a ton of energy but do not penetrate like the buck shot. they are similar in ballistics to a .357 mag but the slug characteristics of flattening reduce penetration but always deliver 100% of the energy where as a big .357 might just pass through. Bird shot would not be great for ducks or such unless you shot em close on the water. But flushing out quail it would work good